<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outerDiv{
            width: 500px;
            height: 304px;
            border:1px solid rgb(112, 136, 112);
            background-color: rgba(0, 255, 255, 0.318);
            margin: 0px auto;
        }
        .innerDiv{
            width:100px;
            height:100px;
            border:1px solid blue;
           float: left;
        }
        /*
        padding内边距
        margin外边距
        */
        .d1{
            background-color:burlywood;
           margin-left: 8px;
           margin-top: 10px;
           margin-right: 8px;
           margin-bottom: 8px;
           padding: 20px;
        }
        .d2{
            background-color: cornflowerblue;
        }
        .d3{
            background-color: darkgoldenrod;
        }

       
    </style>
</head>
<body>
    <div class="outerDiv">
        <div class="innerDiv d1">diva</div>
        <div class="innerDiv d2">divb</div>
        <div class="innerDiv d3">divc</div>
    </div>
</body>
</html>